1. Technical Field
The present disclosure relates to a MEMS device incorporating a fluidic path and to the manufacturing process thereof. In particular, the following description makes reference, without any loss of generality, to assembling of a MEMS pressure sensor of a packaged type.
2. Description of the Related Art
Sensors are known that include micromechanical structures made, at least in part, of semiconductor materials and using MEMS (micro-electro-mechanical systems) technology. Specifically, pressure sensors made using the MEMS technology typically find use in the medical field, in household apparatus, in consumer electronics (cellphones, personal digital assistants—PDAs), and in the automotive field. In particular, in the latter sector, pressure sensors are traditionally used for detecting the pressure of tires of vehicles, and are used by the control unit for signaling alarms. Pressure sensors are used also for monitoring the pressure of air-bags, for controlling the failure pressure of the ABS system, and for monitoring the engine-oil pressure, the fuel-injection pressure, etc.
A MEMS sensor generally comprises a micromechanical detection structure, which transduces a mechanical quantity to be detected (for example, a set of acoustic waves, a pressure, etc.) into an electrical quantity (for example, correlated to a capacitive variation); and an electronic reading circuit, usually made as an ASIC (Application-Specific Integrated Circuit), which performs processing operations (including amplification and filtering) of the electrical quantity and supplies an electrical output signal of an analogue type (for example, a voltage) or digital type (for example, a PDM (pulse-density modulation) signal. The electrical signal, possibly further processed by an electronic interface circuit, is then made available to an external electronic system, for example a microprocessor control circuit of the electronic apparatus incorporating the sensor.
To detect the mechanical quantity, the MEMS structure comprises a membrane formed in or on a semiconductor die and suspended over a cavity. The membrane moreover faces the external environment or is in communication with the latter through a fluidic path, as shown, for instance, in U.S. Pat. No. 8,049,287. filed in the name of the present applicant, disclosing a detection structure including a MEMS pressure sensor, of a differential capacitive type. In particular, in U.S. Pat. No. 8,049,287. the membrane faces a chamber formed in a protective cap fixed at the top to the die or faces a cavity etched from the back of the die and connected with the outside through a hole which extends through supporting elements.
The known MEMS structure, dedicated to detecting differential pressures, may be modified for detecting absolute pressures and may moreover undergo improvement as regards the simplicity of manufacture. In fact, the presence of a hole in the cap typically involves a complex molding of a packaging region, which has to be formed flush with the cap in order to prevent occlusion of the hole therein and is thus generally replaced by bonding of pre-shaped caps. Furthermore, the formation of the membrane facing the rear cavity is difficult to obtain since control of the thickness of the membrane, formed by deep etching from the back of the substrate, is complex.